The invention generally relates to a refractory pouring tube for pouring a molten metal from one metallurgical vessel to another metallurgical vessel. The invention as well relates to a corresponding assembly, comprising such a pouring tube.
It is known in continuous casting of metal melts to use pouring tubes for transferring the molten metal from one metallurgical vessel to another. Such metallurgical vessels comprise ladles, tundishes, ingot moulds etc. During the casting process any contact between the metallurgical melts and ambient air must be avoided.
WO 01/66284 A1 discloses a grooved refractory tube for such purposes. The tube comprises a first end with a first flat contact surface, perpendicular to a longitudinal axis of the tube, and a pouring channel, extending from said first flat contact face towards a second end of the tube, wherein the pouring channel terminates in one or more outlet openings at the second end of the tube. To avoid the entrance of air into the melt flow the first flat contact surface is provided with a so called injection groove. This groove forms, in conjunction with the first contact surface a fluid injection channel which at least partially encircles the said pouring channel.
According to WO 01/66284 A1 this channel may itself become clogged, i.e. blocked during the casting process. This phenomenon has been observed in the case were the injection groove is formed in a surface of a refractory pouring tube bearing against the surface of another refractory component intended to be replaced during casting operations, for example, when the injection groove is formed in the lower surface of an inner nozzle bearing against the upper surface of a pouring shroud or a submerged entry nozzle. Therefore WO 01/66284 A1 proposes to provide an additional groove along the corresponding contact face of said further refractory components, so that at least one of said grooves may operate correctly during casting.
This proposal cannot avoid the risk that one or both of said grooves become blocked during operation which leads to ineffective gas protection and the tendency for air aspiration.
Therefore an object of the present invention is to provide a refractory pouring tube and a corresponding assembly which is/are easy to produce and provide(s) effective means for protecting the metal melt running through said tube against ingress of ambient air.
The invention avoids any of said injection grooves but integrates a gas permeable member into the surface area of the pouring tube being in contact with an associated refractory component. A treating gas, especially an inert gas, is fed into said gas permeable member at a distance to the first flat contact surface. The gas is guided through said member and then leaves the gas permeable member across its upper (free, open) surface which forms part of the first flat contact surface.
During operation, when the second refractory component is arranged in a way where its corresponding contact surface is in direct contact with the first flat contact surface of the tube, the gas, fed under pressure into said gas permeable member, escapes into any slits between the said corresponding contact surfaces and thus avoids the danger of any undesired air entrance.
Similar to the gas provided by a groove the gas provided by the gas permeable member will surround the pouring channel like a curtain, but without any danger of becoming blocked.